This invention refers to the field of the motor-driven manual labour devices. It concerns a chain medium pump for a motor-driven chain saw which sucks the chain medium over a suction pipe from a tank and which delivers it over a pressure pipe to a sawing device of a motor-driven chain saw. Such chain medium pumps are known, for example, from previous applications of the applicant, particularly from U.S. Pat. No. 4,465,440 and EP-BI-0 560 201.
Furthermore, the invention relates to a motor-driven chain saw with a chain medium pump.
For motor-driven chain saws, it is usual, for the lubrification of the chain with a chain medium, especially oil, to provide a special chain medium pump which is driven by the motor of the chain saw and which continuously sucks, during the operation of the saw, a lubrifying chain medium from a store container (tank) and delivers it to the chain where it is brought into contact at an appropriate place with the circulating chain saw.
According to the prior art, most of the time a piston pump is used as a chain medium pump for which a piston working in a cylinder is set into rotation around the piston axle by the motor of the chain saw over a worm gear pair and this rotation is converted into a periodical lifting movement of the piston by appropriate guiding means (for example by a surface being obliquely to the piston axle which which the rotating piston which is prestressed by a spring runs on a guiding pin). Examples of such piston pumps are known from the documents mentioned at the beginning but, for example, also from U.S. Pat. No. 3,938,622, U.S. Pat. No. 5,236,314 or U.S. Pat. No. 4,801,253.
When the chain medium pump is fixedly connected with the motor over the worm gear pair (for example with the crankshaft of a high-speed two-cycle internal combustion engine), it also delivers chain medium to the saw chainxe2x80x94if other measures are not takenxe2x80x94when the saw chain is disconnected from the running motor and stands. However, such a delivery is not wished if the chain is standing. Basically, it would be possible to also disconnect the chain medium pump from the motor through appropriate mechanical devices, when the saw chain is uncoupled. However, such a coupling device is not only complicated and expensive to manufacture but would also require a considerable supplementary space on the chain saw which is constructed as compact as possible and subsequently could not be easily integrated into already existing motor chain saws.
Therefore, the aim of the invention is to create a chain medium pump with which a disconnecting function of the pump can be realized in an easy and space-saving way, the chain being standing, and which only requires slight modifications on existing pump models.
This aim is achieved for a chain medium pump of the type mentioned in the introduction by the fact that, for disconnecting the supply of the sawing device with the chain medium controllable means exist with which the pressure pipe is interrupted, the chain medium pump being running, and simultaneously the chain medium delivered by the chain medium pump can be returned into the suction pipe. Due to the interruption of the pressure pipe and the simultaneous returning of the delivered chain medium to the suction side, the chain medium pump can run further without any impediment, the chain saw being standing, without the chain medium being delivered up to the chain. The chain medium pump over the chain medium in a closed circuit without being exposed to additional loads.
A first preferred embodiment of the chain medium pump according to the invention is characterized in that the controllable means comprise a reverse valve placed in the pressure pipe and a bypass guided by the reverse valve to the suction pipe. Through the reverse valve, an easily operatable space-saving control function with one-valued ON/OFF character is realized. The bypass can easily be integrated into the pump by a few additional elements.
A particularly robust and compact structure of the arrangement is achieved if, according to a second preferred embodiment of the chain medium pump according to the invention, the chain medium pump is placed in a pump case and that the reverse valve and the bypass are integrated into the pump case. Preferably, the reverse valve is configured as a swivelling piston valve to simply and to assure functional safety.
A further preferred embodiment of the chain medium pump according to the invention is characterized in that the chain medium pump comprises a pump piston axially movable in a cylinder bore in the pump case, that, for constituting the reverse valve, a valve bore which is connected with the cylinder bore over a pressure channel is placed in the pump case on the delivery side, valve bore in which a substantially cylindrical valve body with a swivelling piston is placed and swivellably positioned and that the bypass is formed by two through bore holes which discharge within the pump case starting from the valve bore or from the suction pipe at the same level into the cylinder bore and which are connected with each other by a ring groove placed on the pump piston. This type of recirculation can be particularly easily integrated into existing pump concepts if - as described in the documents U.S. Pat. No. 4,465,440 and EP-BI-0 560 201 of the applicant - a pump piston with a ring groove and a through bore are already existing in the pump concepts, because of other reasons, between the pressure pipe and the ring groove.
The swivelling piston preferably has a recess in the form of an axially extending segment of a circle which connects, in a first position of the swivelling piston, the pressure channel with the axially outgoing pressure pipe ; furthermore, the swivelling piston has a connecting groove which connects, in a second position of the swivelling piston, the pressure channel and the first through bore the one with the other.
The motor chain saw according to the invention with a chain medium pump according to the invention is characterized in that the motor chain saw comprises a safety key with which, the motor being running, the sawing device can be activated and desactivated and that the safety key and the controllable means or the reverse valve are operationally connected with each other over actuating means, so that, when releasing the safety key, the pressure pipe is automatically interrupted and, when actuating the safety key, the interruption of the pressure pipe is automatically suppressed. Through the coupling of the disconnectable chain medium pump with the safety key, a triggering function is realized which guarantees a single-valued ON/OFF function and which works practically insensitive to errors and tolerances.
The disconnecting function is triggered by the release of the rear handle of the chain saw, whereby the saw chain still does not have to stand but is, depending on the operator""s habits, still drifting. The effect of this xe2x80x9cadvancedxe2x80x9d disconnection of the delivery of the chain medium is that excess chain medium in the rail connecting area of the chain rail is transported by the drifting chain into the rail. Thus, a draining of the chain medium out of the chain intake area and thus an additional dirt accumulation in the machine is advantageously reduced.
The particular advantage of this triggering consists in that the chain lubrification already begins by actuating the safety key. It is thus assured that the chain medium is already delivered a few seconds before the start running of the saw chain and that the chain is sufficiently lubricated before the operator begins to cut. Furthermore, the use of the safety key offers the advantage that the necessary actuation forces for the valve are practically not perceived by the operator, since they are negligible with respect to the retention force of the machine or to the applied manual force. For the actuation of the valve, a force of, for example, 2 to 5 N is necessary, depending on the lever transmission which is carried out.
According to a preferred embodiment of the motor chain saw according to the invention, the actuating means comprise a Bowden cable which is simple and cheap.
Further embodiments result from the depending claims.